Electron microscope and other instruments are important tools to study the microstructure of materials,often working in a vacuum environment.In order to quickly target the target area measured by the electron microscope,it is necessary to introduce an auxiliary optical microscope to provide a spatial image of the sample area directly.This paper introduces the design of an ultra-high vacuum optical microscope system for direct observation in ultra-high vacuum environment.The optical microscope objective lens has a long working distance of 21.8mm,achieving 40X optical magnification and transverse 1.28μm,longitudinal 1.59μm actually measured high resolution imaging effect,which can assist many kinds of electron microscopy instruments to search the target area.The objective is divided into two groups,the front group is in ultra-high vacuum,the rear group is outside ultra-high vacuum.The distance between two groups is 680mm.And the whole microscopic objective is controlled by the vacuum six-dimensional adjustment frame to scan the target sample,which has a very obvious effect on improving the detection efficiency of the electron microscope.In addition,the microscope can also be used in vacuum mechanical stripping and other systems requiring optical assistance.